Probably they're still piling because chickens are creatures of habit. Do they not roost yet? When you say they're in their own section of a larger coop, does that mean you have adult chickens in the main coop? If so, I would go into the coop in the night and place all of the 8 week olds on the roosts amongst the adult chickens. They'd be toasty warm overnight and no piling. That's what I do with my youngsters when they get confused on cold nights. Check on them early in the morning of course to make sure they're getting along okay, or make sure they have access to something they can hide behind just in case. If you don't have adult chickens, I'd be inclined to move them onto the roost in the warmer coop - be prepared to place them on the roost over and over, and maybe turn off the lamp for a bit, until they give up and go to sleep.